The invention relates to a device for producing relative motion with two translational degrees of freedom between a spindle means and a retaining element.
A spindle means is defined below as any kind of machine tool means which comprises a work spindle for producing rotary notion between a tool and a workpiece in order to machine the workpiece with the tool by means of rotary motion. Without explanations otherwise the term spindle is always defined as the work or main spindle of a machine tool. The rotary motion can be executed either by the tool (for example, in a drill press) or by the workpiece (for example, in a lathe).
To move a spindle means translationally with two degrees of freedom in one plane, in machine tool building conventionally a movement device in the manner of a compound slide is used. In doing so, on a first slide which enables a first translational motion along the first linear axis there is a second slide along with a slide drive in order to enable a second translational movement of the spindle means along a second linear axis which is located conventionally at right angles to the first linear axis. In a movement device designed in the manner of a cross slide for a spindle means all the moments and reaction forces which occur in the machining of a workpiece are transferred both to the drive and guide means of the second slide and also to the drive and guide means of the first slide. This results in that the required machine components of the two linear axes which are built on top of one another must be made with stiff guides or bearings in the form of machine bodies which have been made durable in order to achieve the conventionally desired machining precision. One such movement device is thus necessarily bulky and heavy, the great weight of the masses to be moved limiting the dynamics which can be achieved with one such movement device.
To achieve greater dynamics of the movement devices of the machine tools, in recent years so-called parallel machine kinematics have been developed. In a machine tool which is built using the concept of parallel machine kinematics the drives for the different axes of motion are parallel, this in contrast to the aforementioned movement device in the manner of a compound slide which represents one example of a serial machine kinematics. A movement and positioning device based on parallel machine kinematics for a spindle means is for example shown in FIG. 17 of document EP-A2-0 791 438. A spindle means in the form of a sleeve with a main spindle which is adjustable in the Z-direction is held stationary via eight connecting arms in a support frame. The eight connecting arms are coupled on one end to the rotary spindle unit and on the other end to one slide each. All eight slides can each be moved on a linear guide, the eight linear guides being arranged at right angles to the Z-direction. By means of coordinated displacement of the slides the spindle means can be moved in the X-Y plane which is normal to the Z-direction.
Based on the smaller moved masses, the movement device as in EP-A2 0 791 438 enables greater dynamics than the movement devices mentioned above in the manner of a compound slide. To produce a movement device as in EP-A2 0 791 438 however greater construction effort is necessary. A total of eight linear guides must be arranged precisely to one another and a total of sixteen hinges must be aligned parallel to one another; this is complex in terms of production engineering and is accordingly expensive. Moreover, the construction space which is necessary for the movement device is large relative to the useful working space. Furthermore there arexe2x80x94as is typical for parallel machine kinematicsxe2x80x94certain unfavorable states of the movement device in which for a small motion in a desired direction excessively large compensation motions of individual slides are necessary. This is the case in the movement device as in EP-A2 0 791 438 for example when one connecting arm includes a flat angle with its assigned linear guide and the spindle means must be moved essentially perpendicularly to this linear guide.
The object of this invention is to devise a device for producing relative motion with two translational degrees of freedom between a spindle means and a retaining element. The movement device should be simple to produce and dynamic and moreover should have a high ratio of useful working space to the required construction space.
According to the invention a device for producing relative motion with two translational degrees of freedom between a spindle means with a spindle which bears the first part of a first pair of parts formed from a workpiece and a tool and a retaining element for holding the second part of the first pair of parts has a first base part to which a first part of a second pair of parts which is formed from the spindle means and the retaining element is attached. The movement device furthermore comprises a second base part, at least one of the two base parts can be moved in a straight line with respect to the other along a linear guide with a first translational degree of freedom. A support for carrying the second part of the second pair of parts is coupled to the second base part to be able to swivel by means of a swivel joint around a swivel axis which is located at right angles to the linear guide such that the second part of the second pair of parts can be moved by actuating the swivel joint with a second translational degree of freedom on a circular path.
The reaction forces and moments which are formed in the machining of the workpiece with the tool are accommodated by the swivel joint which is made stiff-and massive. The stiff swivel joint enables articulated motion with exactly one rotational degree of freedom. It offers all other movements largely unyielding resistance based on its stiffness. This guarantees that essentially simply reaction forces are transmitted to a drive means for movement with the second translational degree of freedom (i.e. to a drive means for actuating the swivel joint) and act in the direction of this motion with the second translational degree of freedom. All other reaction forces and moments of the reaction forces and moments which are formed in the machining of the workpiece with the tool are accommodated by the stiff swivel joint. The drive means for the second translational degree of freedom must therefore be made stiff only in that direction in which they actuate the joint. Therefore the drive means for the second translational degree of freedom compared to the corresponding drive means can be made light in a movement device designed in the manner of a compound slide.
In the production of a movement device according to the invention essentially only a single swivel joint must be aligned with great precision at right angles to the linear guide. This means a great simplification of production compared to production of a movement device as claimed in EP-A2-0 791 43. Because the second part of the second pair of parts must be borne by the support from only one side, with a movement device according to the invention moreover a greater ratio of the useful working space to the required construction space can be achieved than with a movement device as in EP-A2-0 791 438.
The linear guide of the movement device of the invention can be located on a base structure. The base structure can consist of a housing of a machine tool, a support frame, an installation platform or another basic structure. It defines simply the reference base for the relative motion of the movement device of the invention. The linear guide can be located on the base structure horizontally, vertically or at any oblique angle. By the arrangement of the linear guide at such a oblique angle in the case of workpiece machining especially advantageous fall of chips can be achieved.
One movement device according to the invention is characterized preferably by drive means for actuating at least one base part which can move along the linear guide, which means comprise a drive spindle which is parallel to the linear guide and a nut which is attached to the moveable base part, the drive spindle and the nut being arranged and made such that they interact in the manner of a spindle-nut drive (preferably of the ball circulating spindle type). But also other suitable drive means can be used for driving the moveable base part along the linear guide, for example drive means in the form of one or more linear motors.
In one preferred embodiment of the invention the support is located on the second base part such that it can be aligned essentially parallel to the linear guide, the direction of the support (or the support means) in the course of this description and claims always being defined as the projection of the direction from the swivel joint to the machining point of the second part of the second pair of parts onto the plane which is normal to the swivel axis, the projection being parallel to the swivel axis.
In one preferred version of the invention the support and the second base part are made such that the support can be swiveled around the swivel axis in an angular range of 90 degrees. In the other preferred version of the invention the support and the second base part are made such that this angular range is 60 degrees. For a given movement device a large angular range creates a correspondingly large useful working space. A large angular range is thus advantageous with respect to the ratio of required construction space to useful working space of the movement device. On the other hand, for a large angular range there are often unfavorable states of the movement device in which for small movements in a certain direction unduly large compensation movements of individual drives are necessary. The best compromise between the useful working space and the small compensation movements depends on the respective application.
In one preferred version with a support which can be aligned parallel to the linear guide, the support and the second base part are made such that the support can be swivelled around a swivel axis in an angular range which is defined by a first angle which deviates by 40 degrees from the parallel direction to the linear guide to a first side and by a second angle of the support direction which deviates by xe2x88x9220 degrees from the parallel direction to the linear guide to the other side. In another preferred embodiment of the invention this angular range is defined by a support direction which deviates by 30 degrees to one side and by xe2x88x9230 degrees to the other side from the parallel direction to the linear guide. Conventionally the swivel motion of the support is limited to one side by a linear guide. In this case, for an asymmetrical angular range of given size the swivel axis (and thus the center of gravity of the movement device) can be nearer at the linear guide than in a symmetrical angular range of equal size. This is advantageous with respect to the stiffness of the movement device. Conversely, by means of a symmetrical angular range a more balanced motion sequence is enabled than in an asymmetrical angular range. Optimization of the angular range depends in turn on the respective application.
Actuating the movement device such that the support direction is always within this angular range guarantees that the movement device cannot assume unfavorable states in which for a small movement of the second part of the second pair of parts in a desired direction unduly large compensation movements by the drive means are necessary. According to another preferred version of the invention the angular range which can be assumed by the support with reference to a parallel to the linear guide is limited even to 45 degrees deviation to one side and to 15 degrees deviation to the other side of this parallel.
Preferably the second base part (to which the support is connected) can move in a straight line along the linear guide. The first base part can then be securely joined to the base structure and even made as an integral component of the base structure.
According to one preferred version of the invention the work spindle of the spindle means, which is held either by the retaining element on the first base part or is borne by the support on the second base part, is located parallel to the swivel axis of the swivel joint, by means of which the support is connected to the second base part. This arrangement has the advantage that it is irrelevant for workpiece machining whether the translational motion which is executed by the second part of the second pair of parts (on a circular path with the swivel axis as the center) with rotational motion (around the swivel axis) is coupled or not, since workpiece machining takes place rotationally symmetrically anyway with reference to the work spindle. The support of a corresponding movement device can then be made especially easily; it can be made as an essentially one-piece arm which is coupled to the second base part by means of only one single swivel joint. This embodiment of the invention can be advantageously used for a drilling spindle or for a sleeve.
According to another preferred version of the invention the work spindle of the spindle means, which is held either by the retaining element on the first base part or is borne by the support on the second base part, is arranged perpendicular to the swivel axis of the swivel joint, by means of which the support is coupled to the second base part. This version of the invention is especially suitable for the case of a vertically arranged linear guide of the movement device.
Preferably the support is made in the manner of a box in order to form a three-dimensional support structure with high stiffness. The support can be made for example essentially as a wedge-shaped box and can be coupled to the second base part in the area of the tip of the wedge. The second part of the second pair of parts is then borne by the support preferably in the area of the foot of the wedge opposite the tip of the wedge.
To actuate the swivel joint an elongated drive lever can be attached on one of its longitudinal ends securely to a support. The drive lever can be attached to the support such that it includes an angle with the latter in the area of the swivel axis. Preferably the support and the drive lever are made essentially as a one-piece rocker, the support forming a first arm of the rocker and the drive lever forming a second arm of the rocker and the rocker being coupled to the second base part of the movement device such that it can be swiveled around the swivel axis in the area of the connecting angle between the two arms.
According to one preferred embodiment of the invention, the movement device has drive means for actuating the swivel joint which comprise a drive spindle (hereinafter also called the articulated drive spindle). Preferably the articulated drive spindle is supported to be able to turn around its axis in bearings which are attached to the second base part in order to drive a nut in the manner of a spindle-nut drive. In the case of a support which is made in the manner of a rocker with one drive lever the nut can be hinged to the drive lever via a deflection mechanism in order to drive the drive lever and thus the support which is securely joined to the drive lever to swivel motion around the swivel axis. Preferably the articulated drive spindle is located parallel to the linear guide for the movable base part. In this case the nut driven by the articulated drive spindle can be guided by a guide which is parallel to the linear guide for the movable base part, and for guidance of the nut driven by the articulated drive spindle either a separate guide or the linear guide of the base part itself can be used.
If in the version of the invention with a movable second base part (on which the support is coupled) the articulated drive spindle is supported on the second base part, the movement device represents serial machine kinematics; the drive means for joint actuation (i.e. for the second translational degree of freedom) are entrained on the base part which can be moved with the first translational degree of freedom. In this arrangement the drives of the two translational degrees of freedom are decoupled from one another: the first translational degree of freedom of the movement device is assigned to the drive means for moving the second base part along the linear guide and the second translational degree of freedom of the movement device is assigned to the joint actuation means.
As an alternative to the serial arrangement of the drives for the two translational degrees of freedom, parallel machine kinematics can also be implemented by supporting the articulated drive spindle to be able to turn around its axis in bearings which, like for example also the linear guide for the first translational degree of freedom, are attached to the base structure. But in this arrangement the drive of the second translational degree of freedom is dependent on the drive of the first translational degree of freedom; if the second base part is moved along the linear guide without simultaneous activation of the articulated drive spindle, at the same time the swivel joint is also actuated and the movement device is moved with the second translational degree of freedom. In the parallel kinematic version of the invention, both for the articulated drive and also for the drive of the movable base part along the linear guide, instead of spindles advantageously a linear drive can be used since they enable much higher advance speeds compared to spindles.
To actuate the swivel joint (i.e., to move the support with reference to the second base part around the swivel axis), instead of the above described joint actuation means also other suitable drive means can be used for driving a swivel joint. Thus the joint actuation means can for example comprise a directly driven round axle. As an alternative the joint actuation means can also comprise any other suitable linear drive which acts between the support and the second base part. For example, this linear drive can consist of a hydraulic lifting device which comprises a piston and a cylinder. As another version the support can be actuated by an articulated drive spindle which is coupled to a second base part around a swivel axis which is parallel to the swivel axis of the support; the drive spindle drives a nut coupled to the support in the manner of a spindle-nut drive.
According to another preferred version of the invention, by means of a second swivel joint a guide arm is coupled to the second base part to be able to swivel around a swivel axis which is parallel to the swivel axis of the support, the guide arm being connected to the support on its longitudinal end facing away from the second base part via a connecting rod which is coupled to the guide arm and also the support such that together with the support it forms a parallelogram connecting rod with a connecting rod which bears the second part of the second pair of parts on a circular path in a translationally movable manner. The embodiment of the invention is advantageous especially when the work spindle of the spindle means is not located parallel to the swivel axis of the swivel joint. Since in this case generally for workpiece machining the rotary position of the second part of the second pair of parts borne on the support with respect to the swivel axis must be considered, decoupling of the motion with the two translational degrees of freedom from the rotary motion of the second part around the swivel axis is desirable. This decoupling is achieved by the parallelogram connecting rod. A movement device according to this preferred embodiment of the invention can be used for example advantageously for machining of a workpiece by means of a vertical work spindle, the vertical work spindle being located essentially parallel to the linear guide means for the first degree of freedom of the movement device.
Another preferred version of the invention is characterized in that the movement device comprises another base part to which by means of another swivel joint another support for bearing another spindle means is coupled to be able to swivel around another swivel axis which is located at right angles to the linear guide such that the other spindle means can be moved by actuation of the other swivel joint translationally on a circular path. In this way a movement device can be formed which is suited for a machine tool built using the twin-spindle concept.
The following detailed description of this invention is used in conjunction with the attached drawings only as an example for better understanding of the invention and should not be interpreted as a limitation of the scope of protection of the patent claims. For one skilled in the art, from the following description in conjunction with the attached drawings and the totality of claims other advantageous embodiments and combinations of features can be easily recognized which however still lie within the domain of this invention. Thus it goes without saying for example for one skilled in the art in the area of machine tool building that the two translational degrees of freedom of the relative motion between a tool and a workpiece can be distributed in any way on the workpiece and the tool.